When optical signals with a very high bit-rate frequency are transmitted over remote transmission paths, e.g. transatlantic paths, chromatic dispersion represents a magnitude that limits the bit-rate frequency and/or the transmission length. A measure of the quality of an optical transmission system is e.g. the product of the bit-rate frequency and the transmission length.
An optical communications transmission system, whose minimum configuration comprises a light source, an optical waveguide and an optical receiver, is generally known.
Chromatic dispersion means that the group velocity, i.e. the velocity at which the optical signal propagates through the optical waveguide, is wavelength-dependent.
This causes each spectral component of a pulse to propagate at a different velocity in the optical waveguide. Thus, depending on its spectral width, a narrowly coupled pulse expands more or less as a result of running time differences. The product of the bit-rate frequency and the transmission length is therefore limited.
The mentioned chromatic dispersion is composed of the material dispersion and the waveguide dispersion. A more elaborate treatment of the dispersion can be found e.g. in the book "Optical Waveguide Technology", by D. Lutzke, Pflaum-Publishers, Munich 1986, pages 35-42.
Commercially available single-mode standard fibers have a zero dispersion wavelength .lambda..sub.0 at about 1.3 .mu.m and so-called dispersion shifted fibers (DSF) at about 1.55 .mu.m. The zero dispersion wavelength .lambda..sub.0 is the wavelength at which the dispersion, indicated in ps/(nm=km), is zero.
Transmission at the zero dispersion wavelength .lambda..sub.0 is desired above all at the highest bit-rate frequencies in conjunction with a remote transmission path, in order to prevent pulse propagation due to the dispersion. This requires precise knowledge of zero dispersion wavelength .lambda..sub.0.
Numerous methods for measuring the chromatic dispersion of optical waveguides are known, e.g. the differential pulse-time delay measurement and the pulse propagation measurement. Such methods are indicated e.g. in E. G. Neumann: "Single-Mode Fibers", Springer-Publishers, 1988, pages 408 to 422.
These methods of determining chromatic dispersion are relatively expensive technologies. For example, for the pulse-time delay measurement, several lasers are required to emit pulses of different wavelengths, and determining the zero dispersion wavelength by approximation methods is subject to considerable measuring inaccuracies.
Carrying out the known methods is particularly expensive if the chromatic dispersion of already dispersed optical waveguide paths must be determined. Dispersed optical waveguide paths are usually spliced partial paths, whose optical waveguides have different zero dispersion wavelengths. This can be due to the production or the environment (e.g. due to temperature, pressure). Determining the average zero dispersion wavelength .lambda..sub.0 of the entire path is thus even more expensive and inaccurate.